Mixed hematopoietic chimerism at day 90 following allogenic myeloablative stem cell transplantation is a predictor of relapse and survival.

We retrospectively analyzed the prognostic significance of mixed chimerism and associated clinical parameters in 80 patients following unmanipulated allogenic stem cell transplantation. Chimerism studies were performed on marrow aspirates using fluorescent in situ hybridization and variable number tandem repeats techniques at day +30, day +90 and +12 months. The median overall survival (OS) was 24 months (range, 1-56 months). Mixed chimerism was found in 23, 28 and 14% of patients at day +30 (1 month), +90 (3 months), and +12 months, respectively. Day +30 chimerism studies failed to provide any prognostic information. Day +90 mixed chimeras (MC) had significantly higher relapse rates compared to day +90 complete chimeras (CC) at 6 months (P=0.03) and 18 months when compared to MC (P=0.03) following transplant. The median OS in day +90 MC and day+90 CC were, respectively (95% CI, 2-35 months), compared to 47 months (95% CI, 20-74 months) (P=0.02). In conclusion, chimerism studies on day +30 could be reserved for patients who fail to demonstrate engraftment. Day +90 MC had higher relapse rates and lower OS, and therefore may be considered for novel therapies and future studies.